If your call has been hacked you won't be able to browse easily on your phone... The browser symbol on your phone won't stable
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user29107Aug 5 '13 at 15:11

What about phone systems at let's say at a hospital for example, and you hear a slight crackle on the line? Is that a symptom that someone has accessed the conversation? Just curious.
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user29147Aug 6 '13 at 8:25

I'm posting as a comment since I haven't verified this information: If the battery gets drained for no reason, if the phone is warm(er) to the touch without you having used it, it's an indication that there's activity that shouldn't be happening on your phone.
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rathAug 6 '13 at 8:48

Unfortunately it may be that the first time you learn that the information is known to someone other than the other person on the call is when you hear it in court. Also, even without a wiretap, the other party to your call may be a mole.
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KeithSAug 5 '13 at 20:30

No, there's no way unless one side is on a very old-school, purely electromechanical system where an end user can detect clicks and pops. These days voice is computer-processed data with tapping built into the software, or in-line taps that are undetectable.

Yeah, the old click/pop detection only works on ancient telephone exchanges built in the '50s and '60s, or taps on the incoming line. This was because they literally tapped the line, often with something as low-tech as crocodile clips. These days everything gets digitised and translated onto packet-switched networks at the local exchange, so the TSPs can just save it to a file. Heck, you could capture and extract the conversation with something as simple as Wireshark and a python script.
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PolynomialOct 1 '12 at 10:18

All true, the thing is that there's still some very old phone equipment out there in some very poor places, but it's really rare!
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GdDOct 1 '12 at 10:36

Yeah, even places with terrible telephone infrastructure (e.g. India) are mainly using switched stuff these days. Then again, in such places you'd never be able to check for clicks and pops, because the line is so terrible you'd get them anyway!
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PolynomialOct 1 '12 at 10:48

So true! The thing is that the old stuff is really hard and expensive to maintain. Plus it takes up huge amounts of space, a warehouse of old electromechanical switches can be services by a single cabinet's new equipment!
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GdDOct 1 '12 at 10:52

1

@GdD An order of magnitude more than that unless sources I've read have gotten their stats crossed. There was one building to rack level consolidation when they replaced electromechanical switches with first generation digital ones; and a second round of consolidation is going on now as the POTS upstream systems are being replaced with IP based telephony.
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Dan NeelyOct 1 '12 at 17:46

In digital communication, for the most part, information is not modified in any way when transmitted over a medium (presuming the use of appropriate noise reduction and error correction schemes). This makes impossible to infer, just by looking at the received data alone, whether the communication was hacked. The only realistic way improve to the security of your connection is by having an elaborate encryption-decryption mechanism on both ends of the communication channel.

To my knowledge there's no such mechanism in place for phone calls. It would be really interesting if companies like AT&T would start offering encrypted channels to VIP users, which would require both the caller and the receiver to have an encryption password for making important calls. If correctly implemented, at least in theory, even the service provider shouldn't be able to tap into the conversations.

From what I've read about this kind of stuff, I think it's probably a good bet to just assume that you're already being tracked, and that every conversation is being recorded (at the very minimum by one governmental agency).

If you are being eavesdropped using an IMSI-Catcher (a fake cell-tower facilitating a Man-in-the-middle attack, in a black van, parked around your house), there are ways to detect them.

One way of doing this is using monitoring-software for special pattern that IMSI-Catchers create in the cell-network. For one typical pattern you need at least two phones for each cell-provider in the area.

IMSI-catcher simulate a network for your phone, but, especially cheaper ones, don't act as a real phone towards the real network. They have various "bugs" like

They just work with outgoing calls. Those can be detected by calling the phone. If the phone isn't reachable, you are being eavesdropped.

They generally use a directive in the GSM-protocol to disable encryption (since it isn't mandatory). Some phones display that with an opened padlock-symbol. Android could probably be modded to display that info :).

Note that if your provider provides the monitoring to whoever, these devices aren't needed, and there's no technical way to detect it.